1. Field of the Invention
This invention relates to a method and apparatus for monitoring the operation of a shaft encoder associated with a rotating shaft and more particularly to a method which provides the capability of undertaking certain self-diagnostic tests relative to the encoder.
2. Description of the Prior Art
A wheel balancing apparatus is disclosed in U.S. Pat. No. 4,285,240, Gold, issued Aug. 25, 1981 commonly owned by the Assignee of the instant invention. The wheel balancer provides for measurement of the unbalance in a rotating body and resolves the unbalance in either one or two planes normal to the axis of rotation to the body. A force transducer is mechanically coupled to a rotating shaft on which the rotatable body is mounted and provides an electrical signal which is indicative of the periodic force at the transducer generated by the unbalance mass in the body during rotation. An analog-to-digital converter receives the electrical signal from the transducer and provides a digital word output which corresponds to the instantaneous magnitude of the periodic force. The system includes a control for the analog-to-digital converter so that the digital words are sampled at a predetermined number of angular increments during each revolution of the rotation shaft. A memory is also provided which contains a plurality of stored digital sine and cosine representative quantities, each of which correspond to one or more of the predetermined angular increments. During the time that the rotating shaft is traversing each of the angular increments the control operates on each of the digital words in accordance with the corresponding sine and cosine representative quantities to provide modified quantities having sine and cosine factors. The quantities including the sine and cosine factors are obtained within an execution time which is reduced by appropriate selection of the stored digital sine and cosine representative quantities. The system sums the modified quantities obtained during excursion through each of the angular increments so that data is provided from which a determination of the unbalance mass magnitude and angular location may be made.